Method of manufacturing commutator segments of compound material

ABSTRACT

Commutator segments are formed by hydrostatically extruding a billet having a core of aluminum or aluminum alloy and a tubular copper or copper alloy casing through a die of such shape that a thin strip is produced. This strip, either during extending or by rolling after extrusion, is given a shape which is thinner in the center than at the edges. The strip is cut longitudinally along its central axis and cut to suitable lengths.

United States Patent 1191 Malm et al. 1 1March 20, 1973 [54] METHOD OF MANUFACTURING 3,620,059 11/1971 Nilsson ..72/60 COMMUTATOR SEGMENTS OF COMPOUND MATERIAL OTHER PUBLICATIONS Inventors: Assar Malm; Jan-Erik Fransson, both of Vasteras, Sweden Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden Filed: May 6, 1971 Appl. No.: 140,687

Assignee:

US. Cl ..29/597 Int. Cl. ..H01r 43/00 Field of Search ..29/597; 72/60; 310/233 References Cited UNITED STATES PATENTS 2/1933 Sorensen ..29/597 8/1919 Doman ....29/597 11/1969 Preece ..29/597 ASEA Inc. Bulletin; Pamphlet AQ 14-106E; covering Production of Copper-Clad Aluminum a New QUIN- TIS Process; September, 1970.

Primary Examiner-Richard J. Herbst Attorney-Jennings Bailey, Jr.

[5 7] ABSTRACT longitudinally along its central axis and cut to suitable lengths.

4 Claims, 4 Drawing Figures P I NIEnmzo 191a 3. 720,998

Fig

Fig 2 Fig.3

M/ENTOR. ASSAR MA LM mn-mm Pam/ 5w METHOD OF MANUFACTURING COMMUTATOR SEGMENTS OF COMPOUND MATERIAL BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing commutator segments of compound material having a core of aluminum and a casing of copper on at least one, but usually three, of the side surfaces of the segment.

2. The Prior Art Usually commutators are built up of segments having substantially wedge-shaped cross-section and consisting of copper or a copper alloy with copper as the main constituent. Experiments have also been carriedout to manufacture commutator segments having substantially rectangular or slightly wedge-shaped frames of a material, normally steel or aluminum, and contact rails of pure copper or a copper alloy applied on one of the narrow sides of the frame. Because of the weight and the forces arising during rotation, which among other things give rise to bending and skewing stresses in the segments and tensile stresses in so-called pressure rings holding together a collector packet, it is desirable to use a light material for the frame. Because of its low weight, aluminum is a suitable material. However, it is extremely difficult to join copper and aluminum satisfactorily. At temperatures above about 450 copper and aluminum form brittle alloys. When copper and aluminum rails are joined by means of welding or soldering, a brittle layer is formed in the contactregion between the materials, which reduces the strength. Copper and aluminum have different coefficients of thermal expansion so that shearing stresses arise in the joint upon temperature fluctuations. The risk of breaking ofwelded or soldered joints is thus considerable.

It has also been proposed to manufacture commutator segments by electrolytically providing one surface on the frame of the commutator segment with a contact surface of copper. However, copper which is applied electrolytically does not have suitable structure and the required strength for commutator purposes. The bond between copper and aluminum is normally also unsatisfactory with electrolytic application. The savings in the quantityof copper have so far not usually outweighed the costs of producing bimetallic commutator segments with low copper content and the inconvenience and risks of using commutators constructed of such segments.

Summary of the Invention The method according to the invention makes it possibleto produce a bimetalliccommutator segment having a core consisting essentially of aluminum and a contact surface consisting essentially of copper which, from the technical point of view, provides a satisfactory replacement for commutator segments of solid copper. Furthermore, in many cases the decreased weightis a considerable advantage. The weight can be reduced by 40 -60 percent depending on the desired wear depthon the segments. The lower weight of the segments causes a reduction in centrifugal forces which, in turn, causes reduced bending andskewing stresses in the segments themselves and less strain on the pressure rings which hold together the stack of segments forming theeommutator. The reduction in stresses permits reduced height of the segment, which is also a saving in material. Usually the outer diameter remains unaltered. It is thus possible to arrange larger cooling channels inside the commutator. A smaller and lighter commutator also involves a lower moment of inertia which, particularly in some cases, may be of great value.

The satisfactory features of the commutator segments are due partly to the direct metallic bond between the copper in the casing and the aluminum in the core or frame and partly to the fact that the frame is surrounded by copper on at least three sides. If the core is surrounded on all sides by copper and the quantity of copper is symmetrically placed, no deformation is caused by temperature fluctuations. Even with threesided, U-shaped copper casings, the copper in the legs of the U contributes to limiting the deformation caused by temperature fluctuations.

In the method according to the invention, the metallic bond between aluminum and copper is obtained by means of isostatic extrusion of a billet having a core of aluminum oran aluminum alloy and a casing of copper or a copper alloy surrounding the core, according to the methods described in Swedish Pat. Nos. 318,540 and No. 327,180, so that a section is obtained which has a large ratio between width and height. After the extrusion, the section is split into two similar sections which are then surrounded by copper on three sides. During the extrusion a rectangular section may be produced, which is rolled to double wedge-shaped cross-section, from which segments having the desired wedge shape are obtained by splitting the section and cutting it intosuitable lengths. It is also possibleduring the extrusion to give the section the desired cross-section directly, thus eliminating one operation.

The method offers a wide selection of material. For instance, a high-strength aluminum alloy may be used in the core and a copperalloy suitable from thepoint of view of wear for the casing. With previous methods of combining these materials, attempts to produce a compound product have been unsuccessful. The casing may consist of acopper alloy containing at least 99 percent copper and silver (Cu Ag) .or some other alloy suitable for commutator purposes. The core may consistof pure aluminum, but a high-strength alloy containing 3.5 5.0% Cu, max. 1.0%Si, max. 1.0% Fe,.0.5 -l.0

costs. The raw material cost of a segment may drop .by

upto percent if there is only a small copper content. Fora commutator segment having a heightof 50 mm and a thickness of 10 mm at the bottom of the U- shaped casing, the costsmay be reduced by 30 -40Ip.ercent.

Brief Description of the Drawings The invention will be described further with reference tothe accompanying drawings.

FIG. 1 shows a side view and FIG. 2 a section of a commutatorsegment produced by the methodaccord ing tothe invention.

FIGS. 3 and 4 show sections of compound material produced by extrusion, which form an intermediate product in the production of segments having the cross section shown in FIG. 2.

Description of the Preferred Embodiments In the drawings 1 designates a commutator segment which is provided at the ends with triangular cuts 2 to receive pressure rings which hold together the segments in a commutator. The segment comprises a core 3 of an aluminum alloy and a U-shaped copper casing 4 which surrounds three sides of the core 3. The thickness of the casing varies. The casing is considerably thinner on the long sides 5 of the core than on its short side 6 which forms the contact surface in a commutator. With a segment height of 50 mm it is possible to obtain a thickness of 10 mm or more on the short side 6 of the segment. The segment is slightly wedge shaped and the wedge incline is chosen so that the planes of the side surfaces meet each other at the center line of a finished commutator. To manufacture the segment, a compound billet is used to start with which consists of an aluminum core and a tubular casing, which are extruded directly to a section according to FIG. 3 having a double wedge-shaped cross-section with the desired cross-section, or to a section according to FIG. 4 which, after the extrusion, is rolled to a double wedge-shaped cross-section according to FIG. 3. The section according to FIG. 3 is then split lengthwise transversely of its width to produce the segment according to FIG. 2.

We claim:

1. Method of manufacturing commutator segments with a core consisting essentially of aluminum and a casing consisting essentially of copper, which comprises hydrostatically extruding a billet of compound material including a core consisting essentially of aluminum and a casing consisting essentially of copper into a strip of relatively thin cross-section compared to its width, whereby to bond the casing and core together, and splitting the strip longitudinally transversely of its width.

2. Method according to claim 1, in which the step of extruding includes making the strip thinner along its longitudinal center line than at its edges.

3. Method according to claim 1, in which the step of extruding includes making the strip of substantially rectangular cross-section, the step of forming the extruded billet to a double wedge-shaped Cross-section before splitting the strip, said cross-section being thinner along the longitudinal center line of the strip than at its edges.

4. Method according to claim 1, in which the step of extruding includes making the material of the casing substantially thicker on the edges of the strip than on its flat sides.

* III I i 3720998 Dated March 20, 1973 4 1 Patent No.

lnventofls) Assar Malrn and Jan-Erik Fransson It is certified that error appears in the above-identified patent v and that said Letters Patent are hereby corrected as shown below:

After the heading, insert:

Claims priority, Application Sweden,

May 6, 1970, 6273/70.

Signed and sealed this 10th day of July 1973'.

(SEAL) Attest:

WARD MgFLETCi-iER JR. Rene Tegtmeyer fi testing Officer Acting Commissioner of Patents FORM PO-10SO (10-69) USCOMNPDC 603764369 u.s. GOVERNMENT PRINTING OFFICE: I969 o-ass-s 

2. Method according to claim 1, in which the step of extruding includes making the strip thinner along its longitudinal center line than at its edges.
 3. Method according to claim 1, in which the step of extruding includes making the strip of substantially rectangular cross-section, the step of forming the extruded billet to a double wedge-shaped Cross-section before splitting the strip, said cross-section being thinner along the longitudinal center line of the strip than at its edges.
 4. Method according to claim 1, in which the step of extruding includes making the material of the casing substantially thicker on the edges of the strip than on its flat sides. 